Initial endocrine therapy (ET) is a common choice for hormone receptor positive (HR+), HER2 negative (HER2-) metastatic breast cancer (MBC) patients for its good tolerability, low toxicity and durable response. The median time to progression (TTP) of initial ET in HR+, HER2- metastatic patients is about 9 months with aromatase inhibitors (AIs). However, all metastatic patients receiving ET will develop resistance to the conventional endocrine treatments ultimately. So some novel agents, like palbociclib and everolimus, are approved to be effective in improving the efficacy of standard ET. But the fact we have to face is either palbociclib or everolimus is focusing on a single checkpoint of pathway that responsible for resistance of ET. In clinical, there are some patients without an activation of resistance-related pathways have poor response to endocrine therapy. And the mechanisms of resistance to endocrine therapy is complicated and not fully understood. So far, these novel agents have not completely solved the clinical problems of secondary drug-resistance. Maybe a broad spectrum anti-cancer therapy with low toxicity and good tolerability is more practical and promising in the near future. Metronomic chemotherapy is administration of low-dose chemotherapy to induce disease control in metastatic cancer patients, which has low-incidence of adverse effects. More and more evidences showed activity of metronomic therapy in breast cancer. Metronomic therapy with or without endocrine therapy in both metastatic and neoadjuvant setting showed considerable efficacy. Although the concept of combination of chemotherapy and endocrine therapy simultaneously was large abandoned because of previous using tamoxifen and intravenous chemotherapy showing no additional benefit, with better understanding of the biology of endocrine therapy and metronomic chemotherapy, it's worth to evaluate whether endocrine therapy plus low-dose metronomic chemotherapy brings a better clinical benefit rate without sacrificing the quality of patients' life. In this phase III study, we investigate the efficacy and safety of low-dose capecitabine plus AI to treat metastatic HR+, HER2- postmenopausal breast cancer patients.